This invention relates to an apparatus for recovering exhaust energy contained in the exhaust gas of an engine. More particularly, the invention relates to an engine energy recovery apparatus for operating, at high efficiency, an exhaust turbine having a generator, thereby improving the exhaust energy recovery efficiency.
Engines having an adiabatic structure have recently come into use. These engines employ an adiabatic material such as a ceramic for constructing engine components like the combustion chambers and exhaust pipe. With engines of this type, it is unnecessary to cool the engine by dissipating the internally generated heat. The energy possessed by the high-temperature exhaust gas, produced by the engine, is recovered and fed back to the engine output shaft, axles and the like to enhance engine output.
One known method of recovering exhaust energy is to reduce the rotational force of a turbine, which is rotated by the exhaust gas, by using a multiple-stage gear mechanism to drive the engine crankshaft.
Another proposal is to effect a series connection between an exhaust turbine having a generator and an exhaust turbine having a compressor for intake, and supply the output of the generator to a motor provided on the engine output shaft, thereby enabling the exhaust energy to be recovered.
Still another proposal is to provide an exhaust bypass circuit; effect the series connection between the exhaust turbine having the generator and the exhaust turbine having the compressor for intake; supply the output of the generator to a motor provided on the engine output shaft; drive the compressor; and control the amount of exhaust that passes through the exhaust bypass circuit, thereby running the engine in an ideal state. These proposals have been disclosed in the specification of Japanese Patent Application Laid-Open (Kokai) No. 59-141712, which describes an engine equipped with an exhaust energy recovery apparatus.
The first method described above of driving the crankshaft by relying upon the gear mechanism involves certain problems. Specifically, the transfer efficiency of one stage of the gear mechanism ordinarily is 90-95%, so that there is a decline in efficiency of about 80% with a three-stage gear mechanism. Furthermore, the rotational speed of an exhaust turbine is a high 10,000 rpm. Reducing this speed requires a gear mechanism having a greater number of stages, thus resulting in a much lower transfer efficiency and a greater amount of frictional loss. Moreover, since the rotational speed of the exhaust turbine is made to accommodate the rotational speed of the engine, optimum engine turbine performance cannot be achieved.
On the other hand, with the proposals described in Japanese Patent Application Laid-Open (Kokai) No. 59-141712, the engine is run in the ideal state by controlling the amount of exhaust gas flowing through the exhaust bypass circuit on the basis of data received from an engine velocity sensor and an engine load sensor. However, no control is performed to optimize the rotational speed of the exhaust turbine or the efficiency of the turbine.